The present invention relates to a developing device and an image forming apparatus. In particular, the present invention relates to a developing device for developing toner to a latent static image to form an image and an image forming apparatus used for a copier, a printer, a facsimile, a multi-function printer (MFP), and the likes.
A conventional image forming apparatus of an electro-photography type such as a printer, a copier, a facsimile, and a multi-functional printer (MFP) is provided with a developing device of a process cartridge type detachably attached to an apparatus main body, thereby improving a maintenance operation. The developing device is integrally formed of a photosensitive drum, a charge roller for charging the photosensitive drum, a developing roller, and a cleaning device.
In recent years, high print quality has been required. Consequently, it is necessary to print an image with high definition and high quality without color shift. To this end, it is necessary to provide each component of an image forming apparatus with high dimension accuracy, high assembly accuracy, and high installation accuracy as well as constant stability.
In general, the developing device includes the developing roller for developing toner on the photosensitive drum. The developing roller is situated at a position contacting with or away from the photosensitive drum by a small distance for attaching toner to a static latent image on the photosensitive drum. A drive device rotates the developing roller. The photosensitive drum and the developing roller are supported on a side plate, i.e., a part of a frame of the developing device.
(Refer to Patent Reference)
    Patent Reference: Japan Patent Publication No. 2006-220875
In the conventional image forming apparatus described above, the frame of the developing device supports both end portions of shafts of the photosensitive drum and the developing roller, and the frame is formed of a plate member. Accordingly, it is difficult to obtain sufficient rigidity against a twisting force applied to the developing device. As a result, when the developing device is assembled, or each roller rotates during a printing operation and causes frictional resistance at a contacting point with respect to an adjacent roller, the developing device may twist and each roller may contact with each other. In this case, a rotational load of the developing device changes, and there is a difference in image quality between left side and right side, thereby increasing the rotational load of the developing device and lowering print quality.
In view of the problem described above, an object of the invention is to provide a developing device and an image forming apparatus, in which it is possible to solve the problems of the conventional image forming apparatus. In the developing device and the image forming device, it is possible to minimize a change in a rotational load and prevent image quality from lowering.
Further objects of the invention will be apparent from the following description of the invention.